The present disclosure relates to a wafer polishing apparatus capable of maintaining a drive ring in a flat state and a wafer polishing method.
In general, a mirror polishing process is performed in a wafer manufacturing process to improve planarization of a wafer, and the most important technology of the planarization technologies is chemical mechanical polishing (CMP).
In the CMP, a semiconductor wafer is polished in contact with a polishing surface while slurry that is a chemical abrasive is supplied to the polishing surface.
The polishing apparatus includes a polishing table having the polishing surface provided with a polishing pad and a pressing head for pressing a semiconductor wafer. When the semiconductor wafer is polished by using the polishing apparatus, a predetermined pressure is applied to allow the semiconductor wafer to contact the polishing pad of the polishing table while the pressing head presses the semiconductor wafer. Here, the polishing table and the pressing head relatively move to allow the semiconductor wafer to contact the polishing surface so that a surface of the semiconductor wafer is planarized and polished to a mirror surface.
Japanese Laid-Open Patent Publication No. 2001-105305 discloses a head assembly structure of a polishing apparatus, which includes a housing and combustible drive ring for forming a pressing chamber in which a predetermined pressure is applied to a lower portion of a spindle shaft to easily support a substrate and adsorbs a wafer onto a bottom surface thereof through various components disposed below the drive ring.
FIGS. 1A to 1B are views illustrating deformation of a drive ring of a head assembly according to the related art.
As illustrated in FIGS. 1A and 1B, in the head assembly according to the related art, a polishing process is performed while the wafer and the polishing pad rotate in directions opposite to each other after the wafer descends up to a polishing pad placed on a platen in a state where the wafer is adsorbed.
In general, the polishing pad used for a final polishing process is constituted by a Nap layer and a base material pad formed of felt. As the polishing process is performed, all of the base material pad and the Nap layer decrease in thickness.
The head assembly descends by a set height to allow the wafer to contact the polish pad, thereby performing the final polishing process. Here, although the drive ring inside the head assembly is maintained in a flat shape at the beginning, as the polishing pad varies in thickness, the drive ring inside the head assembly varies in shape.
When the polishing pad decreases in thickness due to the repeated polishing processes, a central portion of the drive ring 12 is deformed in a concave shape as illustrated in FIG. 1A. As a result, a gap may occur between a sleeve and flange which constitute a wafer mounting part 13, and also, a central axis of the wafer mounting part 13 may horizontally move during the polishing process.
On the other hand, when the polishing pad is newly replaced to increase in thickness, the central portion of the drive ring 12 is deformed in a convex shape as illustrated in FIG. 1B. As a result, a load may be concentrated into an edge portion of the wafer mounting part 13 to increase a polishing amount at the edge portion of the wafer mounting part 13.
As described above, in the wafer polishing apparatus according to the related art, when the polishing pad changes in thickness, the drive ring 12 for balancing the wafer mounting part 13 may be deformed. Therefore, it may be difficult to uniformly maintain polishing quality of the wafer, as well as, polishing performance may be deteriorated.